package com.webside.cdn.utils;

public class Base64 {
	    /**  
	     * Base64编码表。 
	     */  
	    private static final char[] BASE64CODE =  
	        {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V',  
	            'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q',  
	            'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/',};  
	      
	    /**  
	     * Base64解码表。 
	     */  
	    private static final byte[] BASE64DECODE =  
	        {-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  
	            -1, -1, -1,  
	            -1,  
	            -1, // 注意两个63，为兼容SMP，  
	            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, 63,  
	            -1,  
	            63, // “/”和“-”都翻译成63。  
	            52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, 0, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11,  
	            12, 13,  
	            14, // 注意两个0：  
	            15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1,  
	            -1, // “A”和“=”都翻译成0。  
	            -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51,  
	            -1, -1, -1, -1, -1,};  
	      
	    private static final int HEX_255 = 0x0000ff;  
	      
	    private static final int HEX_16515072 = 0xfc0000;  
	      
	    private static final int HEX_258048 = 0x3f000;  
	      
	    private static final int HEX_4032 = 0xfc0;  
	      
	    private static final int HEX_63 = 0x3f;  
	      
	    private static final int HEX_16711680 = 0xff0000;  
	      
	    private static final int HEX_65280 = 0x00ff00;  
	      
	    private static final int NUMBER_TWO = 2;  
	      
	    private static final int NUMBER_THREE = 3;  
	      
	    private static final int NUMBER_FOUR = 4;  
	      
	    private static final int NUMBER_SIX = 6;  
	      
	    private static final int NUMBER_EIGHT = 8;  
	      
	    private static final int NUMBER_TWELVE = 12;  
	      
	    private static final int NUMBER_SIXTEEN = 16;  
	      
	    private static final int NUMBER_EIGHTEEN = 18;  
	      
	    /** 
	     * 构造方法私有化，防止实例化。    
	     */  
	    private Base64()  
	    {  
	    }  
	      
	    /**  
	     * Base64编码。将字节数组中字节3个一组编码成4个可见字符。  
	     *  
	     * @param b  
	     *            需要被编码的字节数据。  
	     * @return 编码后的Base64字符串。  
	     */  
	    public static String encode(byte[] b)  
	    {  
	        int code = 0;  
	          
	        // 按实际编码后长度开辟内存，加快速度  
	        StringBuffer sb = new StringBuffer(((b.length - 1) / NUMBER_THREE) << NUMBER_TWO + NUMBER_FOUR);  
	          
	        // 进行编码  
	        for (int i = 0; i < b.length; i++)  
	        {  
	            code |=  
	                (b[i] << (NUMBER_SIXTEEN - i % NUMBER_THREE * NUMBER_EIGHT))  
	                    & (HEX_255 << (NUMBER_SIXTEEN - i % NUMBER_THREE * NUMBER_EIGHT));  
	            if (i % NUMBER_THREE == NUMBER_TWO || i == b.length - 1)  
	            {  
	                sb.append(BASE64CODE[(code & HEX_16515072) >>> NUMBER_EIGHTEEN]);  
	                sb.append(BASE64CODE[(code & HEX_258048) >>> NUMBER_TWELVE]);  
	                sb.append(BASE64CODE[(code & HEX_4032) >>> NUMBER_SIX]);  
	                sb.append(BASE64CODE[code & HEX_63]);  
	                code = 0;  
	            }  
	        }  
	          
	        // 对于长度非3的整数倍的字节数组，编码前先补0，编码后结尾处编码用=代替，  
	        // =的个数和短缺的长度一致，以此来标识出数据实际长度  
	        if (b.length % NUMBER_THREE > 0)  
	        {  
	            sb.setCharAt(sb.length() - 1, '=');  
	        }  
	        if (b.length % NUMBER_THREE == 1)  
	        {  
	            sb.setCharAt(sb.length() - NUMBER_TWO, '=');  
	        }  
	        return sb.toString();  
	    }  
	      
	    /**  
	     * Base64解码。  
	     *  
	     * @param code  
	     *            用Base64编码的ASCII字符串  
	     * @return 解码后的字节数据     
	     */  
	    public static byte[] decode(String code)  
	    {  
	        // 检查参数合法性  
	        if (code == null)  
	        {  
	            return null;  
	        }  
	        int len = code.length();  
	        if (len % NUMBER_FOUR != 0)  
	        {  
	            throw new IllegalArgumentException("Base64 string length must be 4*n");  
	        }  
	        if (code.length() == 0)  
	        {  
	            return new byte[0];  
	        }  
	          
	        // 统计填充的等号个数  
	        int pad = 0;  
	        if (code.charAt(len - 1) == '=')  
	        {  
	            pad++;  
	        }  
	        if (code.charAt(len - NUMBER_TWO) == '=')  
	        {  
	            pad++;  
	        }  
	          
	        // 根据填充等号的个数来计算实际数据长度  
	        int retLen = len / NUMBER_FOUR * NUMBER_THREE - pad;  
	          
	        // 分配字节数组空间  
	        byte[] ret = new byte[retLen];  
	          
	        // 查表解码  
	        char ch1, ch2, ch3, ch4;  
	        int i;  
	        for (i = 0; i < len; i += NUMBER_FOUR)  
	        {  
	            int j = i / NUMBER_FOUR * NUMBER_THREE;  
	            ch1 = code.charAt(i);  
	            ch2 = code.charAt(i + 1);  
	            ch3 = code.charAt(i + NUMBER_TWO);  
	            ch4 = code.charAt(i + NUMBER_THREE);  
	            int tmp =  
	                (BASE64DECODE[ch1] << NUMBER_EIGHTEEN) | (BASE64DECODE[ch2] << NUMBER_TWELVE)  
	                    | (BASE64DECODE[ch3] << NUMBER_SIX) | (BASE64DECODE[ch4]);  
	            ret[j] = (byte)((tmp & HEX_16711680) >> NUMBER_SIXTEEN);  
	            if (i < len - NUMBER_FOUR)  
	            {  
	                ret[j + 1] = (byte)((tmp & HEX_65280) >> NUMBER_EIGHT);  
	                ret[j + NUMBER_TWO] = (byte)((tmp & HEX_255));  
	                  
	            }  
	            else  
	            {  
	                if (j + 1 < retLen)  
	                {  
	                    ret[j + 1] = (byte)((tmp & HEX_65280) >> NUMBER_EIGHT);  
	                }  
	                if (j + NUMBER_TWO < retLen)  
	                {  
	                    ret[j + NUMBER_TWO] = (byte)((tmp & HEX_255));  
	                }  
	            }  
	        }  
	        return ret;  
	    }  
	}
